Hello to all, please help . i have a 1998 740il , the upper raiator hose gets verry hot , but the lower radiator hose stays cold ! when i remove the radiator cap, and rev up the engine i see that colant rush in the tank , is this meansthe water pump is good? i is this a stuck termostat , please advise how to replace. many thanks Fredwash @aol.com
740il over heating !
Oct 05, 2006
10 Replies
this is generally indicative of a spent thermostat.
How do you figure that? If the coolant flow in the radiator reacts to revving the engine, doesn't that mean the thermostat is open?
Just curious.
Eisboch
Could be a dead water pump. when the plastic impeller and metal shaft part company it might still drag the fan along and cause some flow. But not enough for proper cooling.
Does the 740i V8 engine use a plastic impeller on its waterpump? I thought that mishap was limited to the "small six?"
No, the V8s do it too. At least in the early years.
It is my understanding(limited as that may be :) ) that the thermostat functions as a "door" based on temperature. If the thermostat is stuck closed then the coolant will not be able to flow through the radiatior, cooling the engine. Thereby giving you a very hot upper hose, and a cool lower hose. All the hot stuff stays blocked up by the faulty thermostat.
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